An MRI device is a device which arranges a subject in a uniform static magnetic field space in a shield room, applies a gradient magnetic field and an exciting high frequency magnetic field, receives a magnetic resonance signal generated by using nuclear magnetic resonance with a high frequency coil (RF reception coil), and images an object to be examined. A range in which simultaneous imaging can be performed is limited to the static magnetic field space at maximum, and a range from which a high image quality can be obtained is limited to a sensitivity range of the RF reception coil.
The performances demanded for the RF reception coil include an S/N ratio which determines whether image quality is good or not, the sensitivity range which determines a field of view of an image, and a parallel imaging performance required for higher-speed imaging. The parallel imaging is a method in which a reception coil formed by a plurality of coil elements is used and simultaneous signal measurement is performed, so that an imaging time is reduced. A plurality of rectangular or circular loop coil elements are arranged in a certain direction (a body width direction or a body axis direction), and a phase encoding direction is selected in that direction. The parallel imaging is a technique which can reduce the imaging time to 1/(the number of the coil elements arranged in the phase encoding direction) if the arrangement of the coil elements is the most appropriate. Moreover, by arranging a plurality of loop coil elements two-dimensionally (for example, in the body width direction and in the body axis direction), a reception coil can be realized which can perform higher-speed imaging and has the sensitivity area in a wide range such as the whole body.
The RF reception coil which receives a nuclear magnetic resonance signal can be applied as an RF transmission coil, when an amplifier with a low-output impedance is connected instead of an amplifier for signal detection and amplification with a low-input impedance. Moreover, when a transmission/reception switching circuit is used between the reception amplifier, the transmission amplifier, and the coil, the coil can be used as a coil which can perform both transmission and reception. In the following description, the RF reception coil is described as an RF coil because it can be used not only for reception but also for transmission.
In a case where the wide range such as the whole body is an object to be examined, a technique for imaging the whole body by moving a table table top is used. In this case, seamless imaging can be performed by using a plurality of loop coil elements arranged two dimensionally as described before as an RF coil having a wide sensitivity range. As the RF coil having the wide sensitivity range, an integrated RF coil unit permanently installed on the table top or incorporated in the table top is known. In such an integrated RF coil unit, a plurality of coil elements forming one or more channels are arranged in one housing case in the most appropriate manner to minimize electromagnetic coupling, and a required element is selected, switched, and used.
However, since the integrated RF coil is heavy, there is a problem that a lot of labor is required for detachment. Therefore, in Japanese Patent Application Laid-Open No. 2006-14823 (Patent Literature 1), the coil is taken apart, so that the size and the weight thereof are reduced and the coil can be easily moved from a stand to a place for the coil. More specifically, Patent Literature 1 discloses an RF coil used for receiving a high frequency wave. The RF coil includes a plurality of coil units two or more of which are connected along a predetermined direction and which can be detached. Each of the coil units includes at least one type of first coil element having a shape corresponding to various types of imaged regions, defining one channel, and receiving a high frequency wave from the various types of imaged regions; a portion of at least one type of second coil element having a shape corresponding various types of imaged regions, defining one channel, and, when another coil unit is connected to that coil unit, forming the second coil element for receiving a high frequency wave from the various types of imaged regions together with a remaining portion of the second coil element included in the other coil unit; and a joint portion for joining that coil unit along the predetermined direction. Especially, Patent Literature 1 is characteristic in that the coil units are arranged to be connected in straight portions thereof for making the structure of a connection member of the coil units as simple as possible.